You design something in QCAD. The design has a flaw and is modified accordingly. Six months later you look at the design and can't understand why you made this change.

Suggested Solutions:

There are several common approaches to track changes and revisions in CAD / QCAD, some can even be applied universally for any type of project you are working on:

- Add a visible revision history to the drawing header. This is typically just a short list of the last couple of changes made to the drawing with a date and the name of the person responsible.

- Save each one of your projects into a separate project folder which contains your drawing file(s), a revision history in your favorite format (plain text, spreadsheet, text document, etc.) as well as other drawing related resources (specifications, PDF exports of the drawing, images that belong to the drawing, etc.). This folder is your project portfolio which belongs together as if it were one single file. You can easily ZIP it, back it up, take it with you, etc.It's also recommendable to keep old revisions of your drawings in case you need to roll back to a previous version. You may for example name your folder 'Project X' and your drawing files in it 'Project X 20130114.dxf', 'Project X 20131218a.dxf', 'Project X 20131218b.dxf', etc. or simply 'Project X 001.dxf', 'Project X 002.dxf', etc.

- Add custom properties to individual entities or block references. This is supported since QCAD version 3.4. For example, you can add the properties: 'note' -> 'size increased', 'reason' -> 'improve stability', 'date' -> '20131218' to any entity or block reference.

- Use a professional online or offline revision control system such as git or svn. Both can be installed and used locally or online to track changes of any file types. Online solutions are typically used if multiple people work on the same set of files. Some popular such online services are github.com, bitbucket.org, gitourious.org.